1. Field of the Invention
The present invention relates to a positioning jig for use in manufacturing a power semiconductor module, for example, a semiconductor device manufactured by using the jig, and a method of manufacturing the semiconductor device.
2. Description of the Related Art
FIG. 16A and FIG. 16B show a part of a conventional power semiconductor module 500, wherein FIG. 16A is a plan view and FIG. 16B is a side view seen from the arrow A indicated in FIG. 16A. These figures show intermediate product structure within a resin casing.
The power semiconductor module 500 comprises: an insulated circuit board 53 having a conductive pattern, such as a direct copper bonding (DCB); an IGBT chip 51 and a silicon diode chip 52 soldered onto a conductive pattern 53c of the insulated circuit board 53 having a conductive pattern; a first terminal 54 soldered onto the IGBT chip 51 and the silicon diode chip 52; and a second terminal 55 soldered onto the conductive pattern 53c. The power semiconductor module 500 further comprises bonding wires 57 connecting at one end thereof to gate electrode pads 56 of the IGBT chip 51, and pad electrodes 58 to which the other ends of the bonding wires 57 are connected. Though not depicted, the power semiconductor module 500 is provided with externally leading out terminals connected to the first terminal 54 and the second terminal 55, and control pins soldered to the pad electrodes 58. The power semiconductor module 500 also has a resin casing that seals the whole of the power semiconductor module 500 except for exposing tip portions of the externally leading out terminals and the control pins. The first terminal 54 is connected to the front surfaces of the IGBT chip 51 and the silicon diode chip 52 with solder. The second terminal 55 is connected to the conductive pattern 53c with solder. The front surface and the back surface of the IGBT chip 51 and the silicon diode chip 52 are interposed between the first terminal 54 and the conductive pattern 53c. 
In the process of manufacturing a power semiconductor module 500 mounting an IGBT chip 51 and Si diode chip 52, an intermediate product called a power cell 501 is first assembled. The power cell 501 has the IGBT chip 51 and the Si diode chip 52, the back surfaces of which are soldered on the insulated circuit board 53 having a conductive pattern. The power cell 501 has also a first terminal 54 of a copper lead-frame that is soldered to an emitter electrode 51a of the IGBT chip 51 and an anode electrode 52a of the Si diode chip 52. The power cell 501 further has a second terminal 55 soldered to the insulated circuit board 53 having a conductive pattern. The power cell 501 is tested for its static and dynamic characteristics. The test contributes to improvement of a rate of non-defective units of completed power semiconductor modules 500. The insulated circuit board 53 having a conductive pattern is composed of an insulation plate 53a, a conductive foil 53b on the back surface thereof, and a conductive pattern 53c on the front surface thereof.
FIG. 17 is a plan view of a part of a positioning jig 600 for use in assembling a power semiconductor module 500 of FIG. 16A and FIG. 16B. In the process of assembling a power cell 501 constructing the power semiconductor module 500, a positioning jig 600 is used that is dedicated to each power semiconductor module 500 comprising the components of the IGBT chip 51, the Si diode chip 52, the solder plates (not depicted) for use in soldering the IGBT 51 and the Si diode chip 52, the first terminal 54, and the second terminal 55. Use of the dedicated positioning jig 600 prevents the components from shifting off their positions.
The positioning jig 600 has a first opening 61 for positioning the IGBT chip 51, the Si diode chip 52, and the solder plates (not depicted) used for soldering the IGBT chip 51 and the Si diode chip 52, and a second opening 62 for positioning the second terminal 55. There are three first openings 61 and two second openings 62. Here, description about a positioning jig for positioning the first terminal 54 is omitted because that jig is not involved in positioning of the chips.
Positional shift of the chips is avoided by holding four corners A, B, C, and D of the IGBT chip 51 and the Si diode chip 52 corresponding to the four corners in the first opening 61.
If the soldering process is conducted without using the positioning jig 600 and the IGBT chip 51 and the Si diode chip 52 shift their position, the following step, for example, soldering of the first terminal 54, cannot be conducted, inhibiting manufacture of a power semiconductor module 500. Even if the soldering process is managed to be done, it becomes very hard to achieve designed performance such as current carrying capacity and thermal resistance because of the positional shift.
In addition, if the positional shift is so large that the adjacent chips become in contact with each other, molten solder may run over the chip surface, inviting deterioration of a breakdown voltage.
The patent documents mentioned below disclose examples of using a positioning jig in the process of assembling a power semiconductor module.
Patent Document 1 discloses a semiconductor device in which a first recessed part for mounting a semiconductor chip is formed on a conductive pattern of an insulated circuit board having a conductive pattern. A positioning external terminal used for positioning and connected to the conductive pattern penetrates through a through-hole in a printed circuit board having post pins, thereby positioning the tips of the post pins on a gate pad and an emitter electrode pad of the semiconductor chip. This construction has remarkably improved the positioning accuracy of the post pins on the pad at a low cost. A solder material and a semiconductor chip are mounded on the first recessed part formed in the conductive pattern of the insulated circuit board having a conductive pattern. A solder is placed on a fourth recessed part. Positioning is performed by inserting two dedicated positioning pins connected to the printed circuit board having post pins into the fourth recessed part in the conductive pattern.
Patent Document 2 discloses a mounting jig used for mounting a ball grid allay (BGA) package having a multiple of lands having a solder ball for an electric connection beneath the package onto a printed circuit board. The mounting jig comprises a frame structure that restrains the movement in the direction perpendicular to the mounting direction while allowing the movement in the mounting direction of the BGA package, and that constrains important parts of the periphery of the BGA package. The frame structure has pins capable of engaging to positioning holes formed on the printed circuit board. This construction allows the BGA package to be packaged readily and accurately at a low cost by worker's handling without changing the structure of the BGA package itself. The construction of Patent Document 2 includes the frame structure that has pins linkable to the positioning hole formed in the printed circuit board.
Patent Document 3 discloses a positioning jig having a first jig and a second jig described below.
The first jig has a positioning hole, or an opening, in which a solder sheet and a semiconductor device element can be inserted. The positioning hole is disposed above a circuit board to correspond to a metal circuit. The second jig is able to insert into and remove from the positioning hole. The second jig has a pressing surface that is disposed opposing the metal circuit in a condition of inserted into the positioning hole of the second jig and pressing the semiconductor device element on a solder sheet onto the circuit substrate side. The second jig is positioned by the wall surface of the positioning hole so that the pressing surface is arranged opposing the metal circuit when the second jig is inserted into the positioning hole.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 2012-129336, FIG. 10 and paragraphs 0087-0090, in particular
[Patent Document 2]
Japanese Unexamined Patent Application Publication No. H11-177204
[Patent Document 3]
Japanese Unexamined Patent Application Publication No. 2007-194477
Recently, next generation power semiconductor devices have begun to use silicon carbide (SiC) diodes. The SiC diodes are mainly used for producing smaller chips, for example 3 mm square, than the traditional silicon diodes, because of the higher cost of a SiC substrate than a traditional silicon substrate, and a degraded rate of non-defective units due to defects in the SiC substrate. Large sized chips are readily affected by the lattice defects, lowering the rate of non-defective units and raising the chip cost. As a consequence, a single silicon diode chip is replaced by a multiple of, say six, SiC diodes. Thus, it is needed to connect a multiple of small sized SiC diode chips in parallel.
FIG. 18A and FIG. 18B show construction of a positioning jig 70 having the number of, six in this example, first openings 71 corresponding to the number of small-sized SiC diode chips 81, wherein FIG. 18A is a plan view corresponding to FIG. 17, and FIG. 18B is an enlarged view of the region F indicated in FIG. 18A.
This positioning jig 70 has: three sets of six first openings 71 each for positioning the six SiC diode chips 81, three sets of one second opening 72 each for positioning an IGBT chip 51, and two third openings 73 each for positioning a second terminal 75. As mentioned earlier, description is omitted about the positioning jig for positioning the first terminal, which is not involved in positioning of the chips. Using this positioning jig 70, the four sides of the SiC diode chip 81 are surrounded by the side walls of the first opening 71 and the SiC diode chip 81 is positioned at its four corners corresponding to the four corners of the first opening 71.
However, if the first terminal 74 is connected to the upper surfaces of the six SiC diode chips 81 altogether using this positioning jig 70, the positioning jig 70 becomes unable to be removed after completion of soldering process obstructed by the first terminal 74.
FIG. 19 is a plan view of a part of a positioning jig 90 that is allowed to be removed without obstruction of the first terminal 92. FIG. 19 corresponds to FIG. 18B. The positioning jig 90 has an opening 91 expanding over the whole region beneath the first terminal 92. Any portion of the positioning jig 90 never exists under the first terminal 92. This positioning jig 90 is allowed to be removed after soldering the first terminal 92 without obstruction by the first terminal 92.
However, this positioning jig 90 does not position all of the four corners A, B, C, and D of the SiC diode chip 81 like the positioning jig 70, but positions only three corners A, B, and C leaving the corner D not positioned. Thus, a SiC diode chip 81 floating on the molten solder may move to the position indicated by the dotted line and become in contact with the adjacent SiC diode chip 81. When two SiC diode chips 81 become in contact with each other, the molted solder may run over the front surface of the SiC diode chip 81, causing deteriorated breakdown voltage. Thus, shift of the chip occurs in the process of soldering because the corner D of the SiC diode chip 81 is not positioned, hardly achieving high accuracy positioning of the SiC diode chip 81.
All of the Patent Documents 1 through 3 fail to mention a semiconductor device in which a plurality of small-sized semiconductor chips are connected to both an insulated circuit board having a conductive pattern and a terminal simultaneously through respective joining materials.